Solar PV water pumping study - FINAL REPORT ... - UNDP, Namibia

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Feasibility Assessment for the Replacement of Diesel Pumps with Solar Pumps FINAL REPORT: September 2006 The following losses are added to the hydraulic power to calculate the overall shaft power required: • Pump element efficiency: Variable as a function of the head • Friction losses in the rising main: Variable as a function of the flowrate and the pipe diameter • Rising main losses due to a possibly non-linearity of taper threaded pipes (the quality of taper threaded pipe has become poorer over recent years and there is a good chance that the rising main is not perfectly straight – this “wobble” has efficiency, as well as maintenance implications). This factor can be considerable but is virtually impossible to predict or assess scientifically. It is taken as a fixed 5% value which is considered conservative. • Windage losses: Fixed at 10%. These are friction losses at the entry and exit of the belts into the pulleys. • Derating of the diesel engine for altitude and temperature: Fixed: 20% for 1,300 m altitude (4% per 300m above 100m) and 35°C operatin g temperature (2% for every 5°C above 25°C). The engine load factor is selected at 70%, providing the rated nominal power of the engine. The specific fuel consumption per hour of the particular size of diesel engine is used. The DRWS usually size their diesel engine system for a ten hour pumping day. This still leaves some additional hours in case more water is required and also attempts to use reasonable water abstraction rates for borehole sustainability (instead of pumping the required daily water within two hours, should a borehole have that yield). The costing model allows the pumping intervals and the pumping hours per pumping session to be defined but limits the abstraction rate to 12m 3 /hour. This allows the modelling of diesel pumping systems where the pump may be remotely located from the operator and is thus only operated every second or third day. 3.1.4 Costing The costing of a pumping system that has a life expectancy of a number of years is comprised of the capital cost and the future costs, which include operating cost, maintenance cost and replacement cost. In some life cycle costing calculations a residual value is assumed which will provide a small return for the project again, for example the solar modules or the lead of lead acid batteries. However, this is often something that is far in the future and could be quite arbitrary. In this costing no residual values are considered for a PVP or DP system. Throughout the calculations a differentiation is made between a DRWS installation and a private (commercial farm) installation. The differences are in the capital cost (lower prices for the private system due to owner involvement), the operating costs (more costly for the private system due to a diesel system which can be in the field, away from the home – not applicable to DRWS system) and the maintenance and replacement costs (lower price for the private installation due to more involvement of the owner). There are three transport rates for different services involving transport. The transport rates listed represent the reference case under current fuel prices (N$6.70/litre) and are adjusted proportionally, based on AA rates with increase or decrease of the fuel price. The rates are listed in Table 3.2. Page 18 of 76
Feasibility Assessment for the Replacement of Diesel Pumps with Solar Pumps Table 3.2: Transport rates Transport type FINAL REPORT: September 2006 Rate [N$/km] Truck 9.00 Contractor bakkie 5.00 Local vehicle 3.00 Furthermore there are three distances that are referred to in the calculations. These are: 1. Installation distance: The distance from a larger centre (e.g. Windhoek) to site. It is assumed that the hardware is stocked at that centre. The default distance is 300km one way. 2. Service distance: The distance from the diesel pump installation to the fuel and diesel engine service infrastructure. The default distance is 100km one way. 3. Operator distance: The distance between the operator (farmer) and a remotely located diesel pump. This distance is only applicable to the commercial farmers as it is assumed that the community is always in the immediate vicinity of the installation. The default distance is 3km one way. 3.1.4.1 Capital cost The capital costs occur once at the beginning of the project. It comprises the cost of the equipment and accessories, the cost of the installation and the cost of transport. The cost includes all the accessories up to the exit of the borehole. No pipe extensions, reservoirs or pump house structure are included. In the case of PVPs a dual pump solution can be selected for the Grundfos. This assumes that the borehole is able to accommodate such an installation which exceeds the normal 3 to 4 inch installation diameter of PVPs. The capital costs are nearly doubled in this case as there are only savings on transport and some minor savings on piping if the two pumps feed into the same pipe. It is assumed that the transport vehicle for a PVP installation is a bakkie (N$ 5/km at current fuel prices) whereas the transport vehicle for a diesel installation is a truck (N$ 9/km at current fuel prices) due to the weight of installation materials. It is assumed that the distance to site for the installation trip is 300km. In terms of the DRWS vs. Private system, the main difference is that the DRWS specifications are fairly high and would thus not be a true cost reflection of a private installation. Therefore certain initial cost items are reduced assuming that the commercial farmer will do some of that work at a lower cost (accessories for installation, foundation costs, belt guard, installation cost, transport cost) when the private installation type is selected. The capital costs used in the calculations form part of the spreadsheet database and are listed in the Appendix A2. 3.1.4.2 Operating cost The operating costs for a DRWS installation are only applicable to the diesel pumping system. The operator costs (person starting the diesel engine, person looking after the PVP system) are ignored for both the diesel as well as the PVP installation. Page 19 of 76
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Solar PV water pumping study - FINAL REPORT ... - UNDP, Namibia

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